JP2014061601A - Method for manufacturing optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical element by which generation of internal strain during molding can be reduced, and thereby variation in optical performance can be reduced while favorably maintaining accuracy of an optical surface.SOLUTION: In a second step, a surface to be an optical surface is formed in an initial state in a molten resin MR while a pressurized state of the molten resin MR (pressure retention state) is maintained. In a third step, a mold fastening force is reduced than a predetermined mold fastening force during the pressure retention state in the second step and the reduced mold fastening force is maintained. Then molding is completed in a molding step. Thereby, generation of an internal strain of the molded article can be reduced. An optical element cut out from the molded article shows stable aberration performance while variation in the aberration performance is suppressed.

Description

  The present invention relates to a method for manufacturing a resin-molded optical element used in, for example, an optical pickup device or a laser printer.

  In molding a resin optical element, even an optical element having a high numerical aperture can be provided with a reference surface or a step to suppress misalignment of the optical functional surface (for example, see Patent Document 1), or a mold release inducing portion. It is known that mold release is improved by locally providing (see, for example, Patent Document 2), and during molding, clamping is performed with a constant clamping force (Patent Document 1). , 2). Here, in the case of molding a resin optical element, the elasticity is large and distortion is likely to occur compared to the molding of a glass optical element. Therefore, the necessity of adjusting the clamping force at the time of molding increases.

  However, in the methods of Patent Documents 1 and 2, since the mold clamping force is constant, there is a possibility that stress remains in the molded product to be molded, and internal distortion occurs. In addition, since the degree of such internal strain varies for each product to be molded, even if molding is performed in consideration of the occurrence of internal strain, the internal strain generated between the molded products It is not always possible to suppress variations in optical performance due to distortion. Furthermore, distortion may occur in the gate due to the pressure applied to increase the transferability to the optical surface (pressure holding process). When the distortion reaches the effective diameter of the optical surface, Aberrations will be affected.

JP 2011-156870 A JP2012-45900A

  An object of the present invention is to provide a method for producing a resin-made optical element capable of reducing the variation in optical performance by reducing the occurrence of internal strain during molding while ensuring good accuracy of the optical surface.

  In order to solve the above problems, a method for producing a resinous optical element according to the present invention is a molding method using a molding die having a transfer surface for forming an optical surface of an optical element. A first step of closing the mold to form a molding space; a second step of supplying molten resin to the molding space and holding the molten resin with a predetermined clamping force; and a predetermined step after the second step. The third step of lowering the clamping force to a lower clamping force state and cooling in the lower clamping force state, and the mold was opened in the molding space. And a fourth step of taking out the molded product.

  In the method for manufacturing an optical element, the surface to be an optical surface is formed on the molten resin in an expected state while maintaining a state where the pressure is applied to the molten resin (pressure holding state) in the second step. After that, in the third step, for example, before the solidification of the molten resin proceeds and the molding is completed by cooling, the clamping force in the molding space is made lower than the predetermined clamping force in the pressure-holding state. The molding is completed by setting the state of low clamping force and then completing the solidification of the molten resin to produce a molded product. In this case, by having the third step, it is possible to prevent excessive stress from being applied in the process of molding the molded product, and it is also possible to make the gate distortion less likely to occur. Generation of internal strain can be reduced. Therefore, the optical element cut out from the molded product has a stable aberration performance by suppressing variation in aberration performance. In addition, the optical element has an optical surface with a desired accuracy in which high transfer accuracy is ensured.

  In a specific aspect of the present invention, in the method for manufacturing an optical element, the second step is a molding die having a first clamping force lower than a predetermined clamping force in a state before the molten resin is supplied to the molding space. After the first mold clamping process for clamping the mold, the resin supply process for starting the supply of the molten resin into the molding space in the state of the first mold clamping force, and after the start of the supply of the molten resin in the resin supply process, The mold clamping of the molding die includes a second mold clamping step in which the mold is raised to a second mold clamping force higher than the first mold clamping force and corresponding to a predetermined mold clamping force. In this case, pressure loss at the time of resin filling can be suppressed by supplying the molten resin under a condition of a clamping force lower than a predetermined clamping force.

  In another aspect of the present invention, in the second step, when the mold temperature of the molding die is equal to or lower than a predetermined temperature, the two-step clamping setting by the first clamping process and the second clamping process is performed. Do. In this case, the pressure loss can be suppressed even when the mold temperature at which the pressure loss easily occurs particularly when the resin is filled is low. In particular, pressure loss can be reduced even when the temperature is lower than the normal molding temperature, that is, when the difference from the resin transition point is large and the fluidity is poor.

  In still another aspect of the present invention, in the second step, the first mold clamping force is 20% or more and 70% or less of the second mold clamping force, which is a predetermined mold clamping force. By setting it to 20% or more of the second mold clamping force, it is possible to avoid the occurrence of overpack (resin leakage) due to the mold clamping side losing to the injection pressure. Moreover, by setting it as 70% or less, since air will suitably escape | omit from the clearance gap between metal mold | dies, it becomes difficult to produce an air clogging, and the suppression effect of the pressure loss at the time of resin filling is fully acquired.

  In still another aspect of the present invention, in the third step, the low mold clamping force is 20% or more and 70% or less of the predetermined mold clamping force. By setting it to 20% or more of the second mold clamping force, it is possible to prevent the resin in a state before molding from being excessively deformed and distorted, and by setting it to 70% or less, it is excessive inside the optical element. Can prevent residual stress from remaining, and can sufficiently alleviate the occurrence of internal strain in the molding process.

  In still another aspect of the present invention, in the third step, a low clamping force is brought into a state within a predetermined time after the molten resin starts to be cooled. In this case, the occurrence of internal strain can be mitigated by setting a low clamping force before solidification by cooling proceeds.

  In still another aspect of the present invention, in the third step, the clamping force is brought to a low clamping force within half the time required from the start of cooling of the molten resin to the completion of molding of the molten resin by cooling.

  In still another aspect of the present invention, in the third step, a decrease in the predetermined clamping force is started before the resin inside the molten resin to be an optical element is completely solidified. In this case, it is possible to secure a sufficient time for solidification by cooling after the state of low clamping force.

  In still another aspect of the present invention, the molded article has a plurality of optical elements. In this case, a large number of optical elements can be obtained from one molded product. At this time, by reducing the internal distortion, the thermal history is different because the position on the mold surface is different, and even in the case of multiple cavities that tend to cause aberration variations and aberration fluctuations, The surface shape of each optical element can be made uniform, and variations in surface accuracy between the optical elements can be suppressed.

  In still another aspect of the present invention, the optical element has a numerical aperture of 0.75 or more and / or a diffractive structure. In this case, even in an optical element that has a high design error sensitivity such as a numerical aperture of 0.75 or more and a diffractive structure and that requires a very high surface accuracy, the surface shape of the optical element can be satisfactorily secured. For example, when the optical element is an objective lens for a BD / DVD / CD three-compatible optical pickup device, the tolerance of design error (for example, coma aberration) is very high, and high molding accuracy is required. According to the method of manufacturing an optical element as described above, it is possible to ensure good surface accuracy and reduce the occurrence of coma and the like. Therefore, even with a lens having a very high design error sensitivity such as an objective lens for a BD / DVD / CD compatible optical pickup device, a lens having an accuracy within the design error sensitivity is stably manufactured. It becomes possible. In addition, since the BD objective lens has a large thickness deviation ratio and a thick axial thickness, the influence of internal distortion is noticeable, but aberration can be reduced.

It is a conceptual diagram explaining the shaping | molding apparatus applicable to the manufacturing method of the optical element of 1st Embodiment. (A) is a side sectional view explaining the mold opening state of the molding die incorporated in the molding apparatus, and (B) is the side explaining the mold closing state of the molding die incorporated in the molding apparatus. FIG. (A) is a schematic diagram showing the closed state of the molding die, (B) is a schematic diagram showing injection of molten resin into the molding die, (C), It is a schematic diagram which shows a mode that a molten resin is filled in a shaping die, and is transferred, (D) is a schematic diagram which shows the fall of the clamping force in a shaping die, (E ) Is a schematic view showing a state of mold opening of the molding die. (A) is a graph explaining the change of the distance between metal mold | die, (B) is a graph explaining the change of clamping force, (C) is the screw position accompanying injection | emission of the resin material. It is a graph which shows a change. It is a flowchart explaining the manufacturing method of the optical element using the shaping | molding apparatus shown in FIG. (A)-(D) are the figures for demonstrating the manufacturing method of a comparative example. (A) is a graph explaining a change in mold clamping force, (B) is a graph explaining a change in mold clamping force, and (C) shows a change in screw position accompanying injection of a resin material. It is a graph to show. It is a flowchart explaining the manufacturing method of the optical element of 2nd Embodiment.

[First Embodiment]
Hereinafter, a molding die for injection molding according to a first embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a molding apparatus 100 according to the present embodiment includes an injection molding machine 10 that is a main body part that performs injection molding to produce a molded product MP, and an attached part that takes out the molded product MP from the injection molding machine 10. A certain take-out device 20 and a control device 30 for comprehensively controlling the operation of each part constituting the molding device 100 are provided.

  The injection molding machine 10 is a horizontal molding machine, and includes a molding die 40, a stationary platen 11, a movable platen 12, a mold clamping plate 13, an opening / closing drive device 15, and an injection device 16. The injection molding machine 10 clamps both molds 41 and 42 by sandwiching a first mold 41 and a second mold 42 constituting the molding mold 40 between the fixed platen 11 and the movable platen 12. This enables molding.

  The fixed platen 11 is fixed to the approximate center of the support frame 14 so as to face the movable platen 12, and supports the take-out device 20 on the upper part thereof. The inner side 11a of the fixed platen 11 faces the inner side 12a of the movable platen 12, and supports the first mold 41 in a detachable manner. The fixed platen 11 is formed with an opening 11b through which a later-described nozzle 16d is passed. Note that the fixed platen 11 is fixed to the mold clamping plate 13 via a tie bar so that it can withstand the pressure of mold clamping during molding.

  The movable platen 12 is supported by a linear guide 15a, which will be described later, so as to be movable back and forth with respect to the fixed platen 11. The inner side 12a of the movable platen 12 faces the inner side 11a of the fixed platen 11, and supports the second mold 42 in a detachable manner. Note that an ejector driving unit 45 is incorporated in the movable platen 12. The ejector driving unit 45 is for extruding the molded product MP in the second mold 42 toward the first mold 41 in order to release the molded product MP.

  The mold clamping machine 13 is fixed to the end of the support frame 14. The mold clamping machine 13 supports the movable board 12 from the back via the power transmission part 15d of the opening / closing drive device 15 at the time of mold clamping.

  The opening / closing drive device 15 includes a linear guide 15a, a power transmission unit 15d, and an actuator 15e. The linear guide 15 a supports the movable platen 12 and enables the movable platen 12 to smoothly reciprocate with respect to the advancing and retreating direction with respect to the fixed platen 11. The power transmission unit 15 d expands and contracts by receiving a driving force from an actuator 15 e that operates under the control of the control device 30. As a result, the movable platen 12 moves forward and backward freely with respect to the mold clamping plate 13, close to or away from the mold clamping plate 13. As a result, the fixed platen 11 and the movable platen 12 can be brought close to or separated from each other, and the first mold 41 and the second mold 42 can be clamped or opened.

  The injection device 16 includes a cylinder 16a, a raw material storage unit 16b, a screw drive unit 16c, and the like. The injection device 16 operates at an appropriate timing under the control of the control device 30, and can inject the molten resin from the resin injection nozzle 16d in a temperature-controlled state. The injection device 16 brings the nozzle 16d into contact with a sprue bushing 65 (see FIG. 2), which will be described later, through the opening 11b of the stationary platen 11 in a state where the first mold 41 and the second mold 42 are clamped. The molten resin in the cylinder 16a can be supplied at a desired timing and pressure to a flow path space FC (see FIG. 2) described later.

  A mold temperature controller 46 attached to the injection molding machine 10 circulates a temperature-controlled heat medium in both molds 41 and 42. Thereby, the temperature of both metal mold | dies 41 and 42 can be kept at an appropriate temperature at the time of shaping | molding.

  The take-out device 20 includes an arm 21 that can hold the molded product MP and a three-dimensional drive device 22 that moves the arm 21 three-dimensionally. The take-out device 20 operates at an appropriate timing under the control of the control device 30, and remains in the second die 42 after the first die 41 and the second die 42 are separated and opened. It has the role of gripping the molded product MP and carrying it out.

  The control device 30 includes an opening / closing control unit 31, an injection device control unit 32, an ejector control unit 33, and a take-out device control unit 34. The opening / closing control unit 31 enables the molds 41 and 42 to be closed, clamped, opened, and the like by operating the actuator 15e. In particular, in this embodiment, the value of the fastening force (clamping force) at the time of mold clamping can be changed to a plurality of states according to the setting. The injection device control unit 32 causes the resin to be injected at a desired pressure into the molding space formed between the molds 41 and 42 by operating the screw driving unit 16c and the like. The ejector control unit 33 operates the ejector driving unit 45 to push out the molded product MP remaining in the second mold 42 when the mold is opened from the second mold 42 to release the mold. The take-out device control unit 34 operates the take-out device 20 to grip the molded product MP remaining in the second mold 42 after mold opening and mold release and carry it out of the injection molding machine 10.

  Hereinafter, the molding die 40 will be described. As shown in FIG. 2A and the like, the second mold 42 of the molding mold 40 is capable of reciprocating in the AB direction (direction parallel to the axis AX). As shown in FIG. 2B, the second mold 42 is moved toward the first mold 41, and both molds 41, 42 are mold-matched with the mold-matching surfaces PS1, PS2 and clamped. In addition, a molding space CV for molding the lens and a channel space FC that is a channel for supplying resin to the molding space CV are formed.

  The first mold 41 includes a mold plate 61 disposed on the inner side, that is, on the mold matching surface PS1 side, and a mounting plate 64 disposed on the outer side, that is, on the fixed platen 11 side in FIG. A sprue bush 65 (resin passage) is provided so as to be attached to the first mold 41. The sprue bushing 65 penetrates the first mold 41 in a state of extending substantially parallel to the AB direction that is the mold opening / closing direction.

  The mold plate 61 of the first mold 41 is a metal plate-like member, and includes a plurality of core holes 61a into which the plurality of core molds 62 are inserted, and a sprue hole 66 through which resin flows into the molding space CV. With. A core die 62 is inserted and fixed in each core hole 61a. A plurality of optical transfer surfaces 61e for forming an optical function portion of the lens are formed on the end surface of each core mold 62. Although illustration is omitted, the optical transfer surface 61 e is formed on a circumference centering on the sprue hole 66. When the molded product MP is an objective lens for an optical pickup device, the optical transfer surface 61e has a concave mirror-like first transfer surface S1 for optical surface transfer, and in particular, a BD (Blu-ray Disc). In the case of an objective lens for a 3-compatible optical pickup device of / DVD (Digital Versatile Disc) / CD (Compact Disc), it may have an optical surface provided with a fine structure.

  In addition, in order to keep the temperature of the mold at an appropriate temperature at the time of molding, a temperature control channel for circulating the heat medium, a heater for heating, a thermometer for temperature monitoring, and the like are formed inside the template 61. However, illustration is omitted for simplicity of explanation.

  The mounting plate 64 is a metal plate-like member, and supports the template 61 from behind. The mounting plate 64 supports the template 61 from the opposite side (back side) of the die matching surface PS1 and the optical transfer surface 61e. The mounting plate 64 includes a sprue hole 66 for allowing resin to flow into the molding space CV. The shape of the nozzle touch portion of the sprue hole 66 on the fixed plate 11 side, that is, the sprue bushing 65 is a mortar shape so that the tip of the nozzle 16d fits without a gap. Although illustration is omitted, the mounting plate 64 has a plurality of fastening members for fixing the mounting plate 64 itself to the fixed platen 11.

  The second mold 42 is formed so as to be embedded in the mounting plate 74, the mold plate 71 disposed on the inner side, that is, on the mold matching surface PS 2 side, the mounting plate 74 disposed on the outer side, that is, the movable platen 12 side in FIG. And an ejector member 75.

  The template 71 of the second mold 42 is a metal plate-like member, and includes a plurality of core holes 71 a into which the plurality of core dies 72 are inserted. A core die 72 is inserted into each core hole 71a. A plurality of optical transfer surfaces 71e for forming an optical function portion of the lens are formed on the end surface of each core mold 72. In addition, a cold slug 71b facing the tip of the sprue bush 65 and a runner recess 71f for flowing resin into a molding space CV formed by the optical transfer surfaces 61e and 71e are formed on the end surface of the template 71. Yes. The optical transfer surface 71e faces the optical transfer surface 61e. The runner recess 71f extends from the cold slug 71b toward each optical transfer surface 71e. The runner recess 71f forms a runner Rb of the flow path space FC that communicates with the molding space CV when the first and second molds 41 and 42 are closed (see FIG. 2B). When the molded product MP is an objective lens for an optical pickup device, the optical transfer surface 71e has a concave second mirror-like transfer surface S2 for optical surface transfer, and in particular, BD / DVD / CD 3 In the case of an objective lens for a compatible optical pickup device, the objective lens may have an optical surface provided with a fine structure. A pin hole 71g through which an ejector pin 75a constituting the ejector member 75 is passed is also formed in the template 71.

  In addition, in order to keep the temperature of the mold at an appropriate temperature at the time of molding, a temperature control channel for circulating a heat medium, a heater for heating, a thermometer for temperature monitoring, and the like are formed inside the template 71. However, illustration is omitted for simplicity of explanation.

  The mounting plate 74 is a metal plate-like member, and supports the template 71 from behind. The mounting plate 74 includes pin holes 74g and 74h through which the ejector pins 75a and 75b constituting the ejector member 75 are passed. Although not shown, the attachment plate 74 has a plurality of fastening members for fixing the attachment plate 74 itself to the fixed platen 11.

  In addition, the 1st metal mold | die 41 and the 2nd metal mold | die 42 fit the positioning fitting part 41x provided in the 1st metal mold | die 41, and the positioning fitting part 42x provided in the 2nd metal mold | die 42 by fitting. Positioning in a direction perpendicular to the mold matching surfaces PS1 and PS2 is possible.

  Hereinafter, the manufacturing operation of the molded product MP and the lens LP by the molding apparatus 100 will be described in terms of opening / closing of the molding die 40 and clamping force with reference to FIGS. 3 (A) to 3 (E) and the like. 3 (A) to 3 (E) schematically show one lens and its peripheral part as a part of the molding die 40 shown in FIGS. 2 (A) and 2 (B). For example, the detailed structure of the core portion is omitted. 4A to 4C are graphs showing changes in various numerical values such as clamping force. More specifically, FIG. 4 (A) is a graph for explaining a change in the distance between the first mold 41 and the second mold 42, and shows a state where the mold is opened and a state where the mold is closed. And the state of mold clamping is shown. FIG. 4B is a graph for explaining a change in the value of the clamping force, that is, the fastening force of the molding die 40 in the above operation. FIG. 4C is a graph showing the change of the screw position accompanying the injection of the resin material, that is, the movement of the injection device 16 (see FIG. 1). In addition, the horizontal axis of each graph indicates elapsed time. Note that changes in these various numerical values are appropriately controlled by each control unit 31 of the control device 30 and the like.

  First, as shown in FIG. 3A, the mold 40 in the closed state is fastened with the first mold clamping force indicated by the arrow A1 by the opening / closing drive device 15 (see FIG. 1). Become. This first mold clamping force is weaker than the mold clamping force (second mold clamping force) at the time of transferring the shape described later. The above operation will be described in more detail with reference to FIGS. 4A and 4B. First, as shown in FIG. 4A, the first mold is opened by the opening / closing drive device 15 (see FIG. 1). When the distance between 41 and the second mold 42 is reduced, the mold is closed (time T0), and when the distance is further reduced, mold clamping is started (time T1), as shown in FIG. As shown, the clamping force value begins to rise. When the value of the mold clamping force becomes a certain level or more (time T2), the distance between the first mold 41 and the second mold 42 hardly changes thereafter (see FIG. 4A), but the mold clamping force. The value continues to rise (see FIG. 4B), and the value of the mold clamping force reaches the first mold clamping force (time T3).

  Next, as shown in FIG. 3B, in the state where the first clamping force is reached, injection of the molten resin MR into the molding space CV is started as indicated by an arrow R1. Specifically, as shown in FIGS. 4B and 4C, when the value of the mold clamping force reaches the first mold clamping force (time T3), the screw position in the injection device 16 (see FIG. 1). Begins to change. That is, the injection of the molten resin MR is started by the movement of the injection device 16. Here, as shown from time T3 to time T4 in FIGS. 4B and 4C, the value of the clamping force is the first during the movement of the injection device 16, that is, during the injection of the molten resin MR. It shall be kept constant by the clamping force.

  Next, as shown in FIG. 3C, when the molten resin MR is completely injected into the molding space CV and the pressure is maintained, the clamping force with respect to the molding space CV is changed to the first mold clamping. The force is raised to a relatively strong second mold clamping force (high mold clamping force) indicated by an arrow A2 to the state of the mold clamping force. Here, the second mold clamping force (high mold clamping force) is appropriately set within a range of, for example, 30 to 50 t (tons). Explaining with reference to the graph of FIG. 4B and the like, the injection of the molten resin MR by the movement of the injection device 16 shown in FIG. 4C is completed, and the molding space CV is held in pressure (time). As shown in T4) and FIG. 4B, the opening / closing drive device 15 increases the clamping force again until the second clamping force, which is a value set as the clamping force at the time of transferring the shape, is reached. And the second clamping force set as the clamping force at the time of transfer is reached (time T5). In other words, in order to complete the injection of the molten resin MR and start the transfer of the shape, the mold clamping force for forming the molding space CV is set to the second clamping force. In the state of the second mold clamping force, a good shape is transferred by maintaining the pressure-holding state for the molten resin MR filled in the molding space CV for a certain period of time. The fixed time elapses (time T6), and the heat dissipation of the resin proceeds in parallel with the sufficient transfer of the shape. Here, as shown in FIG. 3D, in the process where the resin is cooled as a result of heat dissipation, the mold clamping force is depressurized, that is, lowered before the resin is solidified and molding is completed. The state of the low clamping force indicated by A3 is assumed. That is, as shown in FIG. 4B, after time T6, the mold clamping force is gradually reduced from the second mold clamping force to a low mold clamping state (time T7), and the second mold clamping is performed. In the state where the mold clamping force is lower than the force, the molten resin MR that has been transferred is subsequently subjected to solidification by cooling, that is, a molding process, whereby the molding process is performed without leaving any internal distortion. Finally, as shown in FIG. 3E, the mold opening operation is performed, and the molded product MP, that is, the lens LP can be taken out.

  In addition, as for molded product MP, as shown, for example to FIG. 2 (A) etc., it is possible to form a some lens radially with a shaping die. That is, one molded product MP has a plurality of optical elements, and a large number of optical elements can be taken from one molded product MP. Specifically, in the molded product MP, the runner portion RP extends radially around the sprue portion SP, and a lens LP is formed on the extension of the runner portion RP. By cutting the gate at the boundary between the runner part RP and the lens LP, individual lenses LP can be obtained.

  Here, for example, as shown in FIG. 3E, the lens LP has an optical function part OP and a flange part FL, and the optical function part OP is an optical transfer surface 61e provided in the molding die 40. , 71e, for example, a first optical surface OS1 formed by the optical transfer surface 61e, and a second optical surface OS2 formed by, for example, the optical transfer surface 71e. The lens LP is an objective lens for a thick type optical pickup device having a large protrusion on the second optical surface OS2 side. Specifically, the lens LP enables reading or writing of optical information corresponding to a BD having a wavelength of 405 nm and a numerical aperture (NA) of 0.75 or more, specifically 0.85. The lens LP is 0.8 ≦ d, where d (mm) is the thickness of the lens LP on the optical axis OA, and f (mm) is the focal length of the lens LP in a light beam having a wavelength of 500 nm or less. /F≦2.0 is satisfied. When the lens LP is an objective lens for a BD / DVD / CD 3-compatible optical pickup device, the second optical surface OS2 is provided with a fine structure such as a diffraction structure. The molded product MP including the lens LP is formed of an optical resin. As the optical resin, for example, COC (cycloolefin copolymer), PMMA (polymenthyl methacrylate) and the like are used.

  Hereafter, each process is demonstrated in detail regarding the manufacturing method of the molded article MP using the shaping | molding apparatus 100, ie, the lens LP, referring the flowchart of FIG. First, the mold temperature controller 46 heats both molds 41 and 42 to a temperature suitable for molding. Thereby, the surface of the mold that forms the molding space CV in both the molds 41 and 42 and the temperature in the vicinity thereof are, for example, 50 ° C. lower than the glass transition temperature of the molten resin MR supplied from the injection device 16. The state is kept heated (step S10).

[First step: Mold closing step]
Next, the opening / closing drive device 15 is operated to advance the movable platen 12 to start mold closing (step S11). By continuing the closing operation of the opening / closing drive device 15, the movable platen 12 moves to the fixed platen 11 side to the die contact position where the first die 41 on the fixed side and the second die 42 on the movable side come into contact with each other. The mold closing is completed. By further continuing the closing operation of the opening / closing drive device 15, mold clamping for clamping the first mold 41 and the second mold 42 with a necessary pressure is started (step S12).

[First mold clamping process]
First, as the first mold clamping stage, by continuing the closing operation of the opening / closing drive device 15, the first mold clamping state in which the molding space CV is clamped with the set first mold clamping force (step) S13). Here, for example, as shown in FIG. 4B, the first mold clamping force is lower than the second mold clamping force set as a value when transferring the shape to the resin in the molding space CV. Is set to a value. The first mold clamping force is more preferably set to 20% or more and 70% or less of the second mold clamping force.

[Second Step: Resin Supply Step, Second Clamping Step and Holding Pressure Maintenance Step]
Next, in the injection molding machine 10, the injection device 16 is operated to bring the nozzle 16d into contact with the sprue bushing 65 of the first mold 41, and as necessary in the molding space CV as shown in FIG. Injection is performed to inject the molten resin MR under pressure (step S14). Here, as described above, during the movement of the injection device 16, that is, the filling of the molten resin MR, the mold clamping force in the molding space CV is maintained in the state of the first mold clamping force (FIG. 4). (See (B)).

  When the filling of the molten resin MR into the molding space CV is completed, as the second mold clamping stage, the opening / closing drive device 15 performs the closing operation again, and as shown in FIG. 4B, the first mold clamping force The value of the mold clamping force in the molding space CV is increased to the set second mold clamping force to set the second mold clamping state (step S15). In the second mold clamping state, the injection molding machine 10 maintains the resin pressure in the molding space CV (step S16), that is, maintains the pressure maintained state (pressure retention maintaining step). At this time, the mold temperature controller 46 appropriately heats the molding space CV and the flow path space FC (see FIG. 2) through which the resin flows into the molding space CV, so that the molten resin MR is injected onto the surface. Transfer in a good state is ensured. In the molding process, the second mold clamping force is preliminarily set as a mold clamping force for forming the molding space CV during transfer of the shape of the molten resin MR so that the occurrence of internal strain can be sufficiently mitigated. It is desirable that it is 95% or more of the set value.

[Third Step: Low Clamping Step and Molding Step]
When the transfer in the second step is sufficient, the heat adjustment gradually adjusts the heating condition so that the heat radiation to the molten resin MR supplied from the injection device 16 gradually proceeds, and the resin is appropriately removed in the molding space CV. This can be achieved (step S17). Here, before the molten resin MR is solidified by cooling by heat radiation and the molding is completed, the opening / closing drive device 15 starts an opening operation for reducing the clamping force, as shown in FIG. 4B. Then, the value of the mold clamping force in the molding space CV is lowered from the second mold clamping force to the set low mold clamping force, and the low mold clamping state is maintained (step S18: low mold clamping process). In this low clamping state, the molten resin MR in the molding space CV is gradually cooled by heat dissipation. Along with such cooling, the molten resin MR is solidified and waits for completion of molding (step S19: molding process). The above low mold clamping force is desirably 20% or more and 70% or less of the second mold clamping force. By setting it to 20% or more of the second mold clamping force, it is possible to prevent the resin in a state before molding from being excessively deformed and distorted, and by setting it to 70% or less, it is excessive inside the optical element. Can prevent residual stress from remaining, and can sufficiently alleviate the occurrence of internal strain in the molding process.

[Fourth process: Mold opening process and removal process]
Next, in the injection molding machine 10, the opening / closing drive device 15 is operated to perform mold opening for retracting the movable platen 12 (step S20: mold opening process). Along with this, the second mold 42 moves backward, and the first mold 41 and the second mold 42 are separated. As a result, the molded product MP, that is, the lens LP is released from the first mold 41 while being held by the second mold 42.

  Next, after the mold is opened, the take-out device 20 is operated to release the molded product MP from the second mold 42 and take it out (steps S21 and S22). Specifically, in the injection molding machine 10, the ejector driving unit 45 is operated to cause the molded product MP including the lens LP and the like to be ejected by advancement of the ejector pins 75a and 75b (extraction process). As a result, the lens LP of the molded product MP is pushed out toward the first mold 41 and released from the second mold 42.

  Finally, the take-out device 20 is operated so that the proper position of the projected molded product MP is held by the arm 21 and carried out to the outside. When transporting the molded product MP, the portion of the molded product MP excluding the lens LP is gripped. The molding of the lens LP is repeated with the above operation as one cycle.

  In addition, during the cooling process of step S17, the weighing operation for the next molding operation is started in parallel with this. In other words, by proceeding with the preparation for the next molding operation during cooling, the cycle time can be shortened when the molding of the lens LP is repeated. In the repetition of molding, the temperature adjustment in step S10 may be performed as necessary.

  According to the method for manufacturing an optical element described above, a state in which pressure is applied to the molten resin MR (pressure holding state) in the pressure keeping step which is a part of the second step is maintained, and the molten resin MR has an optical surface. The surface to be formed is formed in the desired state. Further, in the low mold clamping process, which is the third process, the molding process is completed in the molding process after setting the state of the low mold clamping force lower than the predetermined mold clamping force in the pressure holding state in the second process. Therefore, the occurrence of internal distortion of the molded product can be reduced. Therefore, the optical element cut out from the molded product has a stable aberration performance by suppressing variation in aberration performance. In addition, the optical element has an optical surface with a desired accuracy in which high transfer accuracy is ensured. Further, in the present embodiment, a plurality of optical lenses LP can be taken from one molded product MP. However, due to the configuration described above, the surface shape of each optical lens LP can be changed even in the case of multiple pieces. It can be ensured satisfactorily, and variation in surface accuracy between the optical lenses LP can be suppressed.

  In contrast, FIGS. 6A to 6D are diagrams showing an optical element manufactured by a manufacturing method of a comparative example. In the case of the comparative example, the resin is injected at a high pressure as shown by an arrow A2 in FIG. 6B to the prepared molding die 40 shown in FIG. As shown in FIG. 6, the pressure holding and cooling operations are performed while maintaining the high pressure state, and the product is taken out as shown in FIG. In this case, in the state of FIG. 6C, the molding is performed while the strain such as the internal strain remains. Accordingly, the molded product MP to be manufactured, that is, the optical lens LP, causes variations in aberration performance due to internal distortion, and for example, a difference in height appears on the side end surface of the optical element. In the present embodiment, by suppressing the occurrence of such a situation, it is possible to mold an optical element having a highly accurate optical surface with little difference in height on the side end surface of the optical element.

  Further, in the above, in order to sufficiently suppress the variation in aberration performance due to internal distortion, in the third step, regarding the time from the start of cooling of the molten resin MR until the state of low clamping force, Must be done within a certain range. As an example, it can be considered that a low clamping force state is achieved by half the time required to complete the molding of the molten resin MR by cooling. In addition, the mold clamping force may be lowered before the internal resin of the molten resin MR to be an optical element is completely solidified by cooling by heat radiation of the molten resin MR.

  In the case of the present embodiment, in the second step, the molten resin MR is supplied under conditions of a first clamping force that is a lower clamping force than a second clamping force that is a higher clamping force. Moreover, the pressure loss at the time of resin filling can be suppressed. In particular, by setting the first mold clamping force at 20% or more and 70% or less of the second mold clamping force, it is possible to avoid the occurrence of an overpack (resin leakage) due to the mold clamping side losing to the injection pressure. In addition, the effect of suppressing the pressure loss can be sufficiently exhibited.

  In the present embodiment, the mold temperature differs depending on the resin material used for the molten resin MR. For example, in the case of an olefin resin, the mold temperature can be 125 to 140 ° C. . In the case of the above-described embodiment, by performing the two-stage mold clamping setting by the first mold clamping process and the second mold clamping process, the state is lower than the normal molding temperature, that is, the difference from the transition point of the resin is large. Even in a poor state, pressure loss can be reduced.

[Second Embodiment]
Hereinafter, the manufacturing method of the optical element of 2nd Embodiment etc. are demonstrated. The optical element manufacturing method according to the second embodiment is a modification of the optical element manufacturing method according to the first embodiment, and parts not specifically described are the same as those of the optical element manufacturing method according to the first embodiment. Suppose that The optical element manufacturing method according to the second embodiment is different from the first embodiment in terms of pressure, injection molding timing, and the like in the second step. Since it can be used, illustration and description of the apparatus will be omitted.

  7 (A) to 7 (C) are graphs corresponding to FIGS. 4 (A) to 4 (C) of the first embodiment, and are graphs showing changes in various numerical values such as mold clamping force in the present embodiment. It is. FIG. 8 is a flowchart for explaining each step in detail with respect to the entire manufacturing method of the molded product MP, that is, the lens LP using the molding apparatus 100.

  As shown in the figure, in the present embodiment, the steps up to the pressure keeping step are different from those in the first embodiment. Specifically, referring to FIGS. 7A to 7C, first, as shown in FIG. 7A, the distance between the first mold 41 and the second mold 42 is reduced. From the state of mold closing (time T0), mold clamping is started (time T1) as shown in FIG. 7B, and the value of mold clamping force increases. When the value of the mold clamping force reaches a certain level or more, as shown in FIG. 7C, the injection device 16 starts to move to inject the molten resin MR (time T2). At this time, in this embodiment, as shown in FIGS. 7B and 7C, the value of the mold clamping force continues to increase during the movement of the injection device 16, that is, during the injection of the molten resin MR, By the time when injection of the molten resin MR is completed and immediately before the pressure is maintained (time T3), the mold clamping force is set to a high clamping force set in the opening / closing drive device 15. (Time T4). When reaching the high clamping force, the opening / closing driving device 15 maintains the high clamping force for a certain period of time. Next, when a certain period of time has elapsed (time T5), cooling by heat radiation proceeds, and the mold clamping force is gradually reduced from the second mold clamping force state to a low mold clamping state (time T6), followed by cooling. Is formed by.

  Hereafter, each process of the manufacturing method of molded article MP, ie, lens LP, is demonstrated, referring the flowchart of FIG. First, the mold temperature controller 46 heats both molds 41 and 42 to a temperature suitable for molding (step S10), starts mold closing by the opening / closing drive device 15 (step S11), and starts mold clamping. (Step S12). In the present embodiment, unlike the first embodiment, the mold clamping force is continuously increased without being limited to the first mold clamping force which is a relatively low mold clamping state, and the molding space at the time of transferring the shape of the molten resin MR A state of a high clamping force set in advance as a clamping force for forming the CV is set (step S214). At this time, the molten resin MR is injected into the molding space CV in parallel with step S214. (Step S215), the injection of the molten resin MR is completed immediately after the high mold clamping force is reached.

  Thereafter, the same process as in the first embodiment is performed. That is, the state in which the resin pressure in the molding space CV is maintained is maintained (step S16), the transfer of the injected molten resin MR to the surface in a good state is ensured by appropriate heating, and then the heating is performed. By adjusting the condition, cooling by heat radiation to the molten resin MR supplied from the injection device 16 gradually proceeds to achieve appropriate cooling of the resin in the molding space CV (step S17), and the opening / closing drive device 15 Then, an opening operation for reducing the mold clamping force is started, and the value of the mold clamping force in the molding space CV is lowered from the second mold clamping force to the set low mold clamping force, so that the low mold clamping state is achieved. (Step S18). In this low clamping state, the molten resin MR in the molding space CV is gradually cooled by heat dissipation, and the molten resin MR is solidified to complete the molding (step S19).

  Next, in the injection molding machine 10, the opening / closing drive device 15 is operated to open the mold (step S20). After the mold is opened, the take-out device 20 is operated to release the molded product MP from the second mold 42. (Steps S21 and S22). The molding of the lens LP is repeated with the above operation as one cycle.

  Also in the present embodiment, the surface to be the optical surface is formed on the molten resin MR while maintaining the state where the pressure is applied to the molten resin MR (pressure holding state). Since the molding process is completed after the mold clamping force is lower than the predetermined clamping force in the molding process, the occurrence of internal distortion in the molded product can be mitigated, and the optical with the expected accuracy can be achieved. Thus, an optical element having a stable aberration performance can be manufactured.

  Although the optical element manufacturing method and the like according to the embodiments have been described above, the optical element manufacturing method and the like according to the present invention are not limited to the above, and various modifications are possible. For example, in the above embodiment, the shape of the molding space CV provided in the molding die 40 constituted by the first die 41 and the second die 42 can be various shapes. That is, the shape of the molding space CV formed by the optical transfer surfaces 61e and 71e is merely an example, and can be appropriately changed according to the use of the lens LP and other optical elements. For example, a molding space CV for molding a lens for a laser printer may be formed.

  Further, in the above, when the value of the mold clamping force is increased from the first mold clamping force to the set second mold clamping force, the filling of the molten resin MR is completed and an increase in the mold clamping force is started. Alternatively, the mold clamping force is increased in accordance with the completion timing of filling of the molten resin MR, but the mold clamping timing and the raising degree are the set values that are expected by the timing at which the shape transfer should be started. What is necessary is just to make it be in the state of the 2nd mold clamping force, and various aspects are possible.

  In the above embodiment, the number of lenses LP in the drawing can be four, for example, but may be one or two.

  Moreover, in the said embodiment, although the horizontal shaping | molding apparatus 100 was used, you may use a vertical shaping | molding apparatus.

  Further, in the above embodiment, the molded product MP is ejected by the ejector pins 75 a and 75 b and released from the second mold 42, but may be released by the take-out device 20.

  In the above embodiment, the molded product MP remains in the second mold 42, but may remain in the first mold 41.

DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 11 ... Fixed board, 12 ... Movable board, 13 ... Clamping machine, 15 ... Opening / closing drive device, 16 ... Injection device, 16d ... Nozzle, 20 ... Extraction device, 30 ... Control device, 40 ... Molding Die, 41 ... first mold, 42 ... second mold, 45 ... Ejector drive unit, 61,71 ... Template, 61e, 71e ... Optical transfer surface, 62,72 ... Core mold, 64,74 ... Installation Plate, 65 ... Sprue bush, 75 ... Ejector member, 90, 190 ... Heat shield mechanism, 91 ... Sealing mechanism, 100 ... Molding device, CV ... Molding space, FC ... Channel space, MR ... Molten resin, LP ... Lens, MP ... Molded product, PS1, PS2 ... Molding surface

Claims (10)

A molding method using a molding die having a transfer surface for forming an optical surface of an optical element,
A first step of closing the molding die to form a molding space;
A second step of supplying a molten resin to the molding space and holding the molten resin with a predetermined clamping force;
After the second step, a third step of setting the state of the low mold clamping force lower than the predetermined mold clamping force and cooling in the state of the low mold clamping force;
And a fourth step of taking out the molded product produced in the molding space by opening the molding die, and a method for producing a resin-made optical element.   The second step includes a first mold clamping step of clamping the molding die with a first mold clamping force lower than the predetermined mold clamping force in a state before the molten resin is supplied to the molding space; A resin supply step of starting supply of the molten resin into the molding space in the state of the first mold clamping force; and after the start of supply of the molten resin in the resin supply step, the mold clamping of the molding die And a second mold clamping step of setting the second mold clamping force higher than the first mold clamping force and corresponding to the predetermined mold clamping force. Manufacturing method of resin-made optical element.   In the second step, when the mold temperature of the molding die is equal to or lower than a predetermined temperature, two-stage clamping setting is performed by the first mold clamping step and the second mold clamping step. The method for producing a resinous optical element according to claim 2.   4. The method according to claim 2, wherein, in the second step, the first mold clamping force is 20% to 70% of the second mold clamping force, which is the predetermined mold clamping force. 5. A method for producing a resinous optical element according to one item.   5. The resinous optical according to claim 1, wherein in the third step, the low clamping force is 20% to 70% of the predetermined clamping force. Device manufacturing method.   6. The resinous optical according to claim 1, wherein in the third step, the low mold clamping force is brought into a state within a predetermined time after the molten resin starts to be cooled. Device manufacturing method.   The low mold clamping force state is set in the third step within half the time required from the start of cooling of the molten resin to the completion of molding of the molten resin by cooling. The manufacturing method of the resin-made optical element of description.   8. The method according to claim 6, wherein in the third step, a decrease in the predetermined clamping force is started before an internal resin of the molten resin to be an optical element is completely solidified. A method for producing a resinous optical element according to one item.   The method for manufacturing a resin optical element according to any one of claims 1 to 8, wherein the molded article has a plurality of optical elements.   The method for manufacturing a resin optical element according to any one of claims 1 to 9, wherein the optical element has a numerical aperture of 0.75 or more and / or a diffractive structure.

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